Melt the butter or ghee in a large sauce pan. Add the onions and saute without colouring until softened, about 5 minutes. Add the carrots, squash, celeriac, garlic and tomato paste and saute briefly. Pour over the chopped tomatoes and stock and bring to a gentle boil. Add the sugar and spices and simmer for 20 minutes until the vegetables are soft.
Remove from the heat and use a stick blender to puree until smooth. Return to the heat, add cider vinegar, and salt and pepper to taste. Remove from the heat and finish with a splash of cream, about 2 tablespoons, stirring to combine. Serve with toast and finely chopped parsley.